The present invention relates to a handgrip with a built-in heater for a motorcycle or the like, and more particularly to a handgrip with a built-in flexible printed circuit heater (hereafter simply referred to as the FPC heater), which is a planar heater.
Conventionally, it has been known to incorporate a planar heater in the handgrips of a handlebar of a motorcycle to heat the handgrips as required.
FIG. 12 is a vertical cross-sectional view illustrating an example of a handgrip with a built-in heater of this type (See Japanese Utility Model Application Laid-Open No. 60996/1993). Reference numeral 1 denotes a handgrip body which can be integrally fitted over and secured to a handle pipe 2 as the handle pipe 2 is inserted into the handgrip body 1. The handgrip body 1 has a structure in which a soft rubber cladding layer 5 is molded integrally over the outer periphery of a synthetic resin inner piece 3 which has appropriate rigidity and around which an FPC heater 4 is wound. The inner piece 3, which excels in heat insulation, has a substantially cylindrical shape in which a peripheral portion 3a is formed with slots. The FPC heater 4 extends over the outer periphery of the inner piece 3 over a range covering half the circumference or more but less than the full circumference thereof, so as to efficiently warm the hand of the rider who holds the handgrip. Reference numeral 3b denotes slits formed in the inner peripheral surface of the inner piece 3, and a rubber layer 5a for making pressure contact with the pipe and formed integrally with the soft rubber cladding layer 5 is filled in each slit 3b.
To mold the handgrip body 1, the FPC heater 4 is first wound around the inner piece 3, and a raw rubber sheet 6 is then wound thereon to tentatively secure the FPC heater 4. Then, a core 7 is inserted into the inner piece 3, and this assembly is placed in a fixed mold half 8a, as shown in FIG. 13. Subsequently, a movable mold half 8b is moved toward the fixed mold half 8a, and the mold is closed, as shown in FIG. 14. Then, once the mold halves 8a and 8b have been heated to a predetermined temperature and molten rubber injected into the mold halves 8a and 8b, the raw rubber sheet 6 which tentatively secures the FPC heater 4 is melted by the heat, and is molded integrally with the rubber in the molten state which has flowed into the mold halves 8a and 8b, thereby forming the cladding layer 5 and the rubber layer 5a for making pressure contact with the pipe.
However, with the above-described conventional handgrip with a built-in heater, in light of the fact that the cladding layer 5 is molded by placing the assembly in the mold in a state in which the region indicated at reference character A where no portion of the FPC heater is wound faces the movable mold half 8b, as shown in FIGS. 13 and 14, during the closing of the mold when the movable mold half 8b is engaged with (moved toward) the fixed mold half 8a (see FIGS. 13 and 14), the raw rubber sheet 6 at positions shown at reference characters B.sub.l and B.sub.2 is brought into contact with the vicinities of a parting position of a molding surface between the mold halves 8a and 8b, and is pressed downward in FIGS. 13 and 14. Consequently, there has been a problem in that corner portions at side edges of the FPC heater 4 are turned up, or the FPC heater 4 slides downward along the outer peripheral surface of the inner piece 3, possibly causing a crease in a central portion of the FPC heater in its winding direction, as shown at reference numeral 4b.
FIG. 15 is a development of the FPC heater for showing turned-up portions 4a and the creases 4b occurring during the molding of the cladding layer 5. The turned-up portions 4a and the creases 4b not only constitute direct causes of damage to the FPC heater 4, but also degrade the external appearance of the product if they project outside the cladding layer 5. Hence, it is desirable to ensure that the turned-up portions 4a and the creases 4b do not occur.